Obama's appeal was joined by all 50 members of the Senate's Democratic caucus, who warned that they would consider blocking any appointee from taking office who had been sent to Washington by Blagojevich, who under state law has the power to name Obama's successor.

A day after Obama appeared reluctant to involve himself in the swirling controversy, the president-elect yesterday called on Blagojevich to resign, saying through a spokesman that "under the current circumstances, it is difficult for the governor to effectively do his job and serve the people of Illinois."

Blagojevich was arrested at his Chicago home Tuesday and accused by federal prosecutors of trying to trade his power to appoint Obama's replacement for cash or a lucrative job, and of engaging in other "pay to play" schemes in which state jobs, funds and contracts would be traded for campaign donations. He has denied any wrongdoing.

After being released from federal custody, Blagojevich went to work at his downtown office yesterday morning, pursued by reporters. He did not comment on the government's allegations.

Blagojevich, 52, and his chief of staff, John Harris, 46, have been charged with conspiracy to commit mail and wire fraud and solicitation of bribery. Federal investigators obtained wiretaps on Blagojevich's phone lines, and the governor was intercepted allegedly saying the Senate seat "is a f----- valuable thing, you just don't give away."

Meanwhile, lawmakers who were considered likely choices for Obama's Senate seat were met with speculation about their dealings with Blagojevich. Democratic Rep. Jesse Jackson Jr. of Illinois told reporters in Washington that "I did not initiate nor authorize anyone - at any time - to promise anything to Governor Blagojevich on my behalf."

Jackson's Chicago-based attorney said he believes the congressman is the person identified only as "Senate Candidate 5" in the criminal complaint filed against Blagojevich. In the complaint, prosecutors allege that Blagojevich said he was approached by an intermediary for Senate Candidate 5 who offered to raise $1 million in campaign funds for Blagojevich if the candidate received the appointment.

Jackson, the son of the well-known civil rights activist, said the U.S. attorney's office in Chicago told him Tuesday that he was not a target of the investigation and was not accused of any misconduct. Still, he has retained a lawyer, James Montgomery.

Jackson has been actively seeking the Senate appointment, and he met with Blagojevich about the job Monday. "I presented my record, my qualifications and my vision," Jackson told reporters yesterday. "Despite what he may have been looking for, that's all I had to offer."

Jackson said he still wants the post in the wake of Blagojevich's arrest.

Obama, Sen. Richard J. Durbin, an Illinois Democrat, and others have called for a special election to choose the new senator, although that could leave the seat vacant for months and place the new senator far down the seniority list, behind other new members of the chamber.

Republican Rep. Ray LaHood of Illinois said in an interview that he believes it would be "very difficult" for any candidate who has been tied to the seat, such as Jackson, to remain a candidate for it. "They will be part of a process in which the seat was to go to the highest bidder," LaHood said.

An election would require legislation from the Illinois General Assembly. Until that happens, Blagojevich retains the sole power to fill the seat.

Wary of Blagojevich exercising that power, Senate Majority Leader Harry Reid of Nevada circulated a letter to his fellow Democrats for their signature yesterday that asks Blagojevich to refrain from appointing anyone and calls on him to resign. The letter suggests that Democratic senators could vote to refuse to seat Blagojevich's choice.

In a separate letter, Durbin also asked Blagojevich to step down. In an interview Tuesday, the assistant Senate majority leader had resisted doing so, saying the criminal process needed to play itself out.

Obama's call for Blagojevich to leave office came one day after he had said little about the scandal, except to deny that he ever discussed the vacancy directly with Blagojevich. Citing the continuing investigation, Obama and his transition staff would not disclose whether any aide to Obama spoke to the governor about the seat.